1. Field of the Invention
The present invention relates to a circuit breaker, and more particularly to a circuit breaker with a high breaking capacity provided with two breaking portions.
2. Description of the Related Art
An example of a circuit breaker with a high breaking capacity, known in the prior art is illustrated in FIG. 5. In FIG. 5, the circuit breaker comprises a first breaking portion 50, housed within a space defined by an insulating casing 41 and an insulating cover 42, which are positioned in an upper side of the circuit breaker and arranged to be separable upward and downward respectively. The first breaking portion 50 includes a first fixed contact 43, a first movable contact 44 disposed to make contact with and separate from the first fixed contact 43, an overcurrent tripping device 47 connected in series with the first movable contact 44 through a flexible conductor 45 and having a tripping crossbar 46, and a switching mechanism 48 coupled with the first movable contact 44 and engaged with a pawl 46a of the tripping crossbar 46. The circuit breaker further comprises a second breaking portion 60, housed within an insulating casing 51 which is attached to the back wall of the insulating casing 41. The second breaking portion 60 includes a second fixed contact 53 electrically connected in series with the first fixed contact 43 through a flexible conductor 52, and a second movable contact 55 having a closing spring 54 and disposed in opposition to the second fixed contact 53 to make contact with and separate from the second fixed contact 54.
If a large current such as a short-circuit current flows in the thus arranged current path, the second breaking portion 60 is opened first by an electromagnetic force sufficient to overcome the closing spring 54, and the first breaking portion 50 is then opened by a tripping operation of the overcurrent tripping device 47.
The conventional circuit breaker described above has several disadvantages. First, due to the independent housing of the first and second breaking portions 50 and 60 within the insulating casings 41 and 51 respectively, the circuit breaker is physically large and the current path between the two portions is long. Further, when the current flowing in the second breaking portion 60 is limited in a final breaking step, the electromagnetic repulsion force is reduced and can be overcome by a spring force of the closing spring 54, thereby allowing the second breaking portion 60 to close again. Therefore, only an opening of the first breaking portion 50 can be relied on to achieve the desired breaking of the circuit. Consequently, it has been difficult to manufacture a circuit breaker having a high breaking capacity for use in a high-voltage environment.